Single-channel currents are measured in isolated areas of excitable-cell membranes using the patch electrode method. Channel gating is studied as a stochastic process in cultured rat muscle, mouse spinal cord neurons, and anterior pituitary cells. Gating kinetics are determined for various synaptic agonists and partial agonists acting on the postsynaptic receptors, for electrically excitable channels and for the calcium-induced potassium channel. Electron spin resonance and fluorescence measurements are done on acetylcholinereceptor protein isolated from electroplax in order to develop a molecular probe for the conformation changes induced by agonists.